Bangkok choked for weeks last month, as smog filled the air while military drones and fire trucks fought to bring pollution under control. Schools closed and people were encouraged to stay indoors while others armed themselves with masks.

Meanwhile, the government reached out to citizens to come up with more effective solutions.

Pollution in major Asian cities has become a norm in recent years -- so much so that residents, visitors and policy makers take the situation for granted.

But the deteriorating health of people and life-threatening situations should force us to heed its consequences.

There are thousands of Cambodians working in Bangkok, and the toxicity in the air forced the Cambodian Embassy to urge its citizens to return to the country and urge those who opted to remain behind, to guard their health.

The complacency is particularly apparent in Bangkok, where pollution levels have been worsened by condominiums and the construction of mass transit systems in the city. This year, as the wind dropped off, toxic particles in the air worsened.

It’s clear that urbanization of cities in ASEAN and the rest of Asia has come with incalculable human costs.

New Delhi and Beijing have long suffered pollution and are taking steps to tackle the issue. On the other hand, the people of ASEAN have watched the situation unfold but have yet to take effective remedial action.

The countries of this region are far more interconnected. For instance, seasonal fires in Indonesia due to the open-burning of peat have often resulted in smoke spreading to Singapore and Malaysia.

But what is happening in Bangkok this year has shocked people in the region.

In term of air quality, Bangkok is now considered one of the top 10 polluted cities in the world.

According to Thai media, the amount of fine particulate matter smaller than 2.5 microns (PM 2.5) in some areas, especially along the busiest roadside areas, exceeded the safety limit of 185 micrograms per cubic meter.

PM 2.5 readings measure the concentration of tiny particles less than 2.5 micrometers in diameter -- or about one-30th the diameter of a human hair -- in the air. And long-term exposure to them on a regular basis has been linked to increased risk of death from complications such as cancer or heart disease.

The norms governing the air quality index stipulates that air pollution poses little or no risk if PM 2.5 is between zero to 50 micrograms per cubic meter. However, for some pollutants, there may be moderate health concerns for a very small number of people who are unusually sensitive to air pollution between 51 and 100 micrograms per cubic meter.

It becomes more dangerous if the scale moves to between 101 and 150 micrograms per cubic meter, as people with greater sensitivity could experience a health impact.

If the air quality worsens to 151-200 micrograms per cubic meter, people could start to feel sick and fall ill.

Needless to say, Thailand’s charm was lost as people were forced to wear masks.

Other ASEAN capitals should pay heed.

In Hanoi, Vietnam, the air quality index at various air monitoring stations across the capital has sometimes recorded dangerously high levels. The PM 2.5 concentration in Hanoi was recently 400 micrograms per cubic meter in some areas, particularly along the busy Pham Van Dong Street.

With all the construction going on in Jakarta, it will surely be next on the list.

Media in the country have reported that the PM 2.5 level in the city throughout 2016 and 2018 was above the ambient air quality standard of 15 micrograms per cubic meter set by Jakarta’s administration.

In Manila, the Philippines, though some people have shared concerns about the air quality, the problem is not considered serious yet.

Kuala Lumpur in Malaysia and Singapore are among the world’s top 100 most livable cities for Asian expatriates, but some experts warn that air pollution could be an issue in the future.

Likewise, with other ASEAN cities growing, air quality will be an issue elsewhere in the region, too.

Bandar Seri Begawan, the capital of Brunei with a population of some 100,000, may not generate serious pollution, but Phnom Penh, the capital city of Cambodia, Vientiane, the capital city of Laos, and Yangon, the commercial capital of Myanmar, should make preparations for the future.

Growth trends in Phnom Penh, Vientiane and Yangon are expected to be very high in coming years.

According to the Ministry of Environment of Cambodia, the PM 2.5 rate in Phnom Penh is 35.36 micrograms per cubic meter.

However, the city already has 1.5 million permanent residents, and construction sites can be found across the city, while the number of vehicles has increased every year -- a situation not dissimilar from Vientiane and Yangon.

At a glance, the air quality in most of the capital cities in ASEAN may seem passable but it could get dangerous, if all city governments do not pay adequate attention.

An integrated approach to tackle the air pollution issue is needed, along with a regional mechanism established in all ASEAN capitals first, in an effort to deal with the issue.

Khan SophiromKhan Sophirom is an assistant to the editor-in-chief of the Rasmei Kampuchea Daily. The Asian Writers’ Circle is a series of columns on global affairs written by top editors and writers from members of the Asia News Network and published in newspapers and websites across the region. -- Ed.